1. Field of the Invention
The present invention relates to an apparatus and a method for testing semiconductor integrated circuits at an elevated temperature.
2. Description of the Related Art
In the semiconductor device fabrication process, after a plurality of integrated circuits are formed on a semiconductor wafer, they are tested in the wafer state, before the wafer is diced into individual integrated circuits or ‘chips’. Such tests are conventionally carried out by positioning the wafer on the test stage of a wafer prober, contacting the electrode lead pads of the integrated circuits with probe pins disposed on a probe card mounted in the wafer prober, and measuring the electrical characteristics of the integrated circuits. This type of test enables each semiconductor integrated circuit (chip) to be identified as good or bad, so that defective chips can be screened out.
The tests carried out using this type of wafer prober are generally performed at an elevated temperature, such as 100 degrees Celsius or more. It is therefore necessary to heat the semiconductor wafer to the prescribed temperature before the test begins and maintain it at the prescribed temperature during the test. For effective heating, a heater is often incorporated into the chuck that holds the wafer.
High-temperature electrical tests are also carried out on tape-mounted semiconductor integrated circuits, such as chip-on-film (COF) and tape-carrier-package (TCP) semiconductor integrated circuits. These tests are conventionally carried out by a chip handler equipped with a probe card and a hot air blower.
When high-temperature electrical tests are performed as described above, only the semiconductor wafer or only the semiconductor integrated circuits are heated directly. The probe card is separated from the heat source (heater or air blower nozzle) and is heated only indirectly, so its temperature rises more slowly. In the test process using a wafer prober, the probe card is not heated at all when the wafer chuck is moved away from the test stage. One consequent problem is unwanted cooling of the wafer by the probe pins, making it is difficult to test the integrated circuits at the intended temperature, because the test starts with the probe card at a relatively low temperature. Another problem is inadequate thermal expansion of the probe card, making it necessary to readjust the positions of the probe pins, a process that lengthens the test time.
These problems are addressed by Miki et al. in Japanese Patent Application Publication No. 2000-241454 and by Kawazoe in Japanese Patent Application Publication No. 2000-138268. Both publications disclose a heater attached to a reinforcing plate or holder that holds the probe card, to heat the reinforcing plate or holder, thereby heating the probe card. A problem is that the probe card is still heated only indirectly; much of the heat generated by the heater is dissipated by the reinforcing plate or holder, resulting in wasted energy and higher than necessary heating costs.
Another problem is that the heater is conventionally not turned on until the probe card is mounted, so it takes time for the heater itself to reach the necessary temperature, and then takes further time for the necessary amount of heat to begin reaching the probe card through the reinforcing plate or holder. The resulting lengthened test times lead to higher test costs per wafer or per chip.
An alternative solution, proposed by Carlin et al. in U.S. Pat. No. 5,124,639, is to provide a heating element in the probe card itself, but this increases the cost of the probe card, again leading to higher test costs.